1. Field of the Invention
The present invention relates to a relay server and more specifically to a relay server that enables communication to be performed between terminals connected to different LANs (Local Area Networks).
2. Description of the Related Art
Conventionally, a communication technology called a virtual private network (Virtual Private Network, VPN) has been known (for example, see Japanese Patent Application Laid-Open No. 2002-217938). The VPN is used for, for example, performing communication via the Internet between terminals that are connected to LANs of a plurality of branch offices (stations) each located in different regions. Use of the VPN enables another LAN located in a distant place to be used as if it is a directly-connected network.
In this type of system, communication between terminals is performed with use of IP addresses (private IP addresses) of terminals that are connected to LANs. The IP addresses are assigned without any overlap in the same LAN, but may overlap among terminals that are connected to different LANs. In such a case, two or more identical IP addresses exist in the VPN, which makes it impossible to perform proper communication.
To avoid such a situation, it is necessary that, when there are overlapping IP addresses, the VPN is once terminated (or alternatively apparatuses having the overlapping IP addresses set therefor are logged out of the VPN), and then re-setting of IP addresses is performed. However, the re-setting of IP addresses affects other apparatuses that are connected to the same LAN. Therefore, changing the IP address may not be practical in some LANs. In this point, improvement has been demanded in the VPN.